Angioplasty has become widely accepted as an efficient and effective method for opening stenoses in the coronary arteries and in other parts of the vascular system. The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, the physician guides the catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying a fluid under pressure through an inflation lumen to the balloon. The inflation of the balloon causes stretching of the artery and pressing of the lesion into the artery wall to re-establish acceptable blood flow through the artery.
One important characteristic of a dilatation catheter used for angioplasty is its profile, i.e., the outer diameter of the distal end portion of the balloon. Considerable effort has been spent in developing low-profile dilatation balloon catheters by minimizing the dimensions of the core or inner tube which extends through the balloon to its distal end, and by reducing wall thicknesses, to the extent possible, of the balloon itself.
Another important consideration is the outer diameter of the catheter in its deflated condition. This outer diameter affects the ease and ability of the dilatation catheter to pass through a guide catheter and through the coronary arteries leading to the stenosis to be opened.
In order to reduce the outer diameter of the balloon catheter in its deflated condition, it is common to fold or wrap the flaps of the deflated balloon. When inflation fluid is applied to the deflated balloon, it causes the balloon flaps to unwrap so that the balloon can inflate to its fully inflated condition.
In the prior art, it has been common to use a balloon protector in conjunction with a balloon dilatation catheter. A balloon protector serves at least two important functions. First, it protects the balloon and distal tip of the catheter from possible damage during shipping. Second, the balloon protector keeps the balloon tightly wrapped in its deflated condition to minimize the outer diameter of the balloon in its deflated state.
A balloon protector is typically applied to the distal end portion of the catheter prior to sterilization of the catheter. The sterilization process can involve exposing the catheter, with the balloon protector in place, to an elevated temperature for a period of time.
With certain balloon materials, the sterilization process will advantageously cause the balloon to be heat set in the folded or wrapped configuration in which it is held by the balloon protector. As a result, when the balloon protector is later removed, the balloon remains in this tightly wrapped or folded configuration. The heat setting of a balloon has the further advantage that when the balloon is inflated and then deflated, as it may be several times during an angioplasty procedure, the application of negative pressure during deflation will cause the balloon to return to its tightly wrapped heat set configuration. This greatly facilitates the removal of the catheter after the procedure has been performed.
Various types and configurations of balloon protectors have been shown in the prior art, for example, in U.S. Pat. Nos. 4,738,666 and 4,710,181 to Fuqua, in U.S. Pat. No. 5,053,007 to Euteneuer, in U.S. Pat. No. 5,066,298 to Hess, in U.S. Pat. No. 5,116,318 to Hillstead, and in U.S. Pat. No. 4,540,404 to Wolvek.
The above-noted Fuqua '666 and '181 patents propose a catheter protector comprising a hollow cylindrical sheath. The Fuqua sheath covers the entire length of the catheter, and is removed by pulling it off of the proximal end of the catheter. Fuqua also proposes providing perforations in the sheath for facilitating its removal. A similar arrangement is proposed in the above-referenced Wolvek '404 patent, in which a sheath is slidably disposed over a substantial section of a catheter body, covering the balloon disposed at the distal end of the catheter body. The sheath and catheter assembly are advanced into the patient's vascular system until the distal balloon end is positioned in the area to be dilated. The sheath is long enough that its proximal end remains exposed outside of the patient, such that the sheath may be withdrawn along the catheter body until the balloon is uncovered. Then, the dilatation procedure can be performed.
The above-noted Euteneuer '007 patent proposes a compression protector employing an inner sleeve applied over a deflated balloon, an outer sleeve applied over the inner sleeve, and a compression housing for compressing the outer sleeve radially in on the inner sleeve, thus compressing the inner sleeve radially in on the balloon. With the balloon thus compressed within the Euteneuer '007 protector, the catheter is then sterilized at an elevated temperature. The inner and outer sleeves are formed of materials which exhibit heat-shrink qualities such that the heat treatment causes the balloon to be further compressed to a smaller outer diameter. The Euteneuer '007 protector is removed just prior to introduction of the catheter into the patient, with the balloon retaining its compressed form as a result of the heat treatment.
The above-noted Hess '298 patent proposes protecting a catheter's balloon by wrapping the balloon with tape in an overlapping fashion. In a manner similar to that proposed in the Euteneuer '007 reference, the Hess '298 balloon is subjected to heat treatment after being wrapped, in order to further compress the balloon and affect a heat-setting of the balloon in its compressed condition.
In the above-referenced Hillstead '318 patent, there is proposed an elastic sleeve for covering the balloon of a catheter used for placement and expansion of an expandable intraluminal stent. The Hillstead sleeve is provided to facilitate withdrawal of the balloon from the intraluminal stent.
As catheter distal sections, including catheter balloons, have become smaller, thinner, and more fragile, it has become increasingly difficult to apply a balloon protector which does not damage the catheter or the balloon and yet wraps the balloon as tightly as possible. This is particularly true with balloon protectors which take the form of hollow cylindrical tubing, which can be quite difficult to slide over a wrapped balloon.
To overcome such difficulties, it has been proposed in the prior art to use a low-friction material, such as Teflon.TM. or the like, for a hollow cylindrical balloon protector, such that the difficulty in sliding the protector over the wrapped balloon is minimized. Notwithstanding such proposals, however, there is perceived by the inventor to be a continuing need for improved balloon protectors for dilatation balloon catheters.